1. Field of the Invention
This invention to a method of modifying the formation of difficultly removable deposits in waste heat recovery plants of glass furnaces, particularly soluble silicate furnaces, which facilitates removal of such deposits.
2. Statement of the Related Art
Glass and soluble silicates (waterglass) are generally produced in tank furnaces with regenerative firing (i.e., open-hearth furnaces). In this process, the waste gases which emanate from the combustion of fossil fuels in the tank furnaces and which normally contain sulfur compounds, for example, SO.sub.2 or SO.sub.3, leave the heat exchange chambers of the furnaces at temperatures of 450.degree. to 700.degree. C.
The heat content of these waste gases is often used for steam generation in a subsequent waste heat recovery plant employing steam boilers with tubular heat exchangers. In the course of the heat exchange process, these waste gases (which contain relatively large quantities of solids in supposedly evaporated form, such as alkali metal sulfates and alkali metal disulfates), are cooled to temperatures of 200.degree. to 250.degree. C. A large proportion of the evaporated solids desublimates during the cooling process and is deposited on the heat exchanger tubes in the form of a firmly adhering, heavily encrusted, and solid coating.
This coating, which becomes increasingly thicker, impairs heat transfer after only a short time so that the waste heat recovery plant operates increasingly less efficiently.
To ensure effective heat transfer in the heat exchanger tubes of the steam boilers, the insides of the tubes have to be cleaned at least once a day. The coatings which, in the case of soluble silicate furnaces, consist primarily of alkali metal sulfates and alkali metal disulfates and which are formed through desublimation of the evaporated solids present in the waste gases, are very solid, adhere firmly to the tube surfaces and, mechanically, can only be removed with considerable difficulty, often involving damage to the tube walls. For this reason, some heat recovery plants of the type in question are cleaned by spraying them internally with hot water. However, because of the highly acidic alkali metal disulfates, serious corrosion problems arise after the cleaning work has been conducted.